The invention relates to a method of connecting two short-wave transmitters in parallel to an aerial which is divided into two halves, each half being fed by a separate transmitter. A phase discriminator is provided to monitor the difference in phase between the transmitters and to generate an output signal which supplies information for the correct phase regulation.
Such methods have long been in use. If two transmitters are to run in parallel in the short-wave range, then, as a result of the difficulty of realizing a short-wave parallel-connection bridge, the aerial must be divided into two halves, each half being fed by a separate transmitter. In order to be able to avoid an unwanted "slewing", that is to say an undesirable alteration in the radiation direction of the combined aerial, the phase of the two transmitter signals must be adjustable and must be able to be checked.
At present, the monitoring is effected by means of a phase discriminator and the phase rotation is effected by means of a manually adjustable phase shifter between the oscillator and one of the two transmitters, while the second transmitter is fed directly from the same oscillator. Thus the synchronism in frequency is assured. Despite the considerable size of the short-wave frequency range, the realization of the phase discriminator does not involve any major problems. Nevertheless a broad-band phase-rotation circuit is very extensive and relatively expensive.
The foregoing method has been found to be unsuitable for remote-controlled transmitter installations for the following reasons:
(1) under certain circumstances, the transmitters have different phase rotations in the cold and in the warm state;
(2) remote-control channels are required for remote control of the phase regulation;
(3) the regulation must be constantly checked which requires additional operational expense; and
(4) the ambiguity between 0 degrees and 180 degrees must be eliminated by a sensing system since the system can be adjusted 180.degree. out of phase.